A traditional whisky cask is a bilge-barrel shape, formed by a plurality of curved staves that result in an overall bulge when it is assembled and bound together. Such a bulge (bilge) is useful for manually rolling and controlling the direction of the cask, which may weigh 500 kg or more, on its side.
Casks for spirits can be made of any suitable material; however, whisky casks are required to be made from oak which is important for the maturation process. It is typically found that after several uses (e.g. at intervals of ten years when a new batch of spirit is introduced to the cask for maturation) the interior wood of the cask must be “rejuvenated” by flailing the surface (e.g. by wire brush) in contact with the spirit. As such an average barrel normally has a lifespan of 50 years.
The general design of whisky casks in common use, made from oak, has not changed significantly in many hundreds of years, although some attempt has been made to introduce new designs over the years. For example,    Patent Citation 0001: GB 1136469 A (GEORGE RICHARD MORRIS; ALVA DONALD MESSENHEIMER). Dec. 11, 1968.describes a square ended barrel with the intent to save space in a warehouse; since square shapes can pack together more efficiently than a circular/cylindrical shape that must necessarily have empty gaps therebetween.
However, GB1136469 in fact describes a “cabinet” construction and not a cask in the traditional sense. The staves of the cabinet must have a jointing mechanism and rely on an elastomeric bonding agent for sealing and cohesion.
A particular problem experienced with traditional cask designs, i.e. casks that do not utilise bonding and/or sealing agents, is that when warehoused (e.g. palletised upright or high racked on their bilge; in both cases up to six levels high) the staves can be forced apart by sheer weight, causing slow loss of spirit. Loss is also observed at the area of the bung where whisky is introduced/removed from the barrel.